Breaking change: The required keyword argument on most aioxmpp.xso descriptors has been removed. The semantics of the default keyword argument have been changed.
Before 0.3, the XML elements represented by descriptors were not required by default and had to be marked as required e.g. by setting required=True in xso.Attr constructor.
Since 0.3, the descriptors are generally required by default. However, the interface on how to change that is different. Attributes and text have a default keyword argument which may be set to a value (which may also be None). In that case, that value indicates that the attribute or text is absent: it is used if the attribute or text is missing in the source XML and if the attribute or text is set to the default value, it will not be emitted in XML.
Children do not support default values other than None; thus, they are simply controlled by a boolean flag required which needs to be passed to the constructor.
The class attributes SERVICE_BEFORE and SERVICE_AFTER have been renamed to ORDER_BEFORE and ORDER_AFTER respectively.
The aioxmpp.service.Service class has additional support to handle the old attributes, but will emit a DeprecationWarning if they are used on a class declaration.
See aioxmpp.service.Meta.SERVICE_AFTER for more information on the deprecation cycle of these attributes.